1. Field of the Invention
The present invention relates to a window glass antenna device having a defrosting heater and a radio signal receiving antenna which are composed of thin wires or line patterns on a window glass panel of an automobile, and more particularly to a window glass antenna device including an antenna dedicated to an electronic key system on an automobile.
2. Description of the Prior Art
Conventional electronic key systems for use on automobiles allow doors, glove boxes, and trunk lids to be opened and closed under remote control using a transmitter unit carried by the user. Specifically, when operated by the user, the transmitter unit transmits a radio control signal, which is received by an antenna on the automobile body to cause the electronic key system to open or close the doors, the glove box, or the trunk lid.
There has been known a window glass antenna device having a defrosting heater and a radio signal receiving antenna which are composed of thin wires or line patterns on a window glass panel of an automobile, the defrosting heater or the radio signal receiving antenna being shared by an electronic key system.
FIG. 5A of the accompanying drawings shows a conventional window glass antenna device including a radio signal receiving antenna that is shared by an electronic key system, and FIG. 5B of the accompanying drawings shown another conventional window glass antenna device including a defrosting heater that is shared by an electronic key system.
In FIG. 5A, a window glass antenna device 21 comprises a window glass panel 22, a defrosting heater 23, and a radio signal receiving antenna 24, which is shared as an electronic key system antenna 25 by an electronic key system. The defrosting heater 23 and the radio signal receiving antenna 24 are disposed on the window glass panel 22. An amplifier 26 is connected to the window glass antenna device 21 for amplifying AM and FM radio waves received by the radio signal receiving antenna 24 and also amplifying a electronic key system control radio wave received by the electronic key system antenna 25. A power supply 27 such as a battery is also connected to the window glass antenna device 21 for supplying electric energy to the defrosting heater 23.
The defrosting heater 23 comprises a plurality of heater wires in the form of thin Nichrome (trade name) wires or a line pattern of printed and baked silver paste. The heater wires are connected at opposite ends to bus bars 23a, 23b which are connected through feeder terminals 23c, 23d, respectively, to the power supply 27 through a capacitor 30.
The radio signal receiving antenna 24 comprises a plurality of thin conductive wires or a line pattern of printed and baked silver paste.
The amplifier 26 is connected to a feeder terminal 24a that is connected to the radio signal receiving antenna 24, i.e., the electronic key system antenna 25. AM or FM radio waves received by the radio signal receiving antenna 24 or a control radio wave received by the electronic key system antenna 25 is detected and amplified by the amplifier 26, which outputs an AM or FM radio signal 26b and a control signal 26a.
Since the radio signal receiving antenna 24 is shared by the electronic key system, the AM or FM radio waves and the control radio wave received thereby tend to interface with each other, resulting in a reduction in the antenna performance. In addition, a long period of time is needed or additional parts are required to tune the radio signal receiving antenna 24 to different frequencies used in different geographical regions where automobiles with the window glass antenna devices are sold.
In FIG. 5B, a window glass antenna device 31 is similar to the window glass antenna device 21 shown in FIG. 5A except that the feeder terminals 23c, 23d of the defrosting heater 23 are connected through a choke coil 29 to the power supply 27, and the feeder terminal 24a of the radio signal receiving antenna 24 is connected through a DC blocking capacitor 28 to the amplifier 26. The defrosting heater 23 is shared as an electronic key system antenna 25 by an electronic key system. The choke coil 29 provides a high impedance for enabling the electronic key system antenna 25 to efficiently receive a control radio wave, and a low resistance to allow electric energy to be supplied efficiently from the power supply 27 to the defrosting heater 23.
A control radio wave which is received by electronic key system antenna 25 is transmitted as a control signal to the radio receiving antenna 24, and then supplied from the feeder terminal 24a through the DC blocking capacitor 28 to the amplifier 26. The amplifier 26 detects and amplifies the control signal, and outputs a control signal 26a.
Since the defrosting heater 23 is shared by the electronic key system, a long period of time is needed to tune the electronic key system antenna 25 to different frequencies used in different geographical regions where automobiles with the window glass antenna devices are sold. Furthermore, the window glass antenna device shown in FIG. 5B requires the chock coil 29 and the DC block capacitor 28 as additional parts.